Control with column loaded strip



Nov. 18, 1952 .H F, CLARK 2,618,721

CONTROL um COLUMN LOADED STRIP WMM Nov. 18, 1952 H. F. CLARK 2,618,721

CONTROL. wrm comm Loman s'mzp' Filed June 16, 1945 2 Sl'iEETS-S-IEEI- 2BwyjNI/TOR. :9 M WMM Patented Nov. 18, 1952 M 2.618.721 coN'raoL wrmCOLUMN LOADED s'rmr Harry F. Clark, Oakwood, Ohio, assignor to GeneralMotors Corporation, Dayton, Ohio, a corporation of Delaware ApplicationJune 16, 1945, Serial No. 599,791

(Cl. 20D-122) Claims. a 1 This invention relates to electrical apparatusand more particularly to motor starting and overload controls forelectric motors.

Because of their apparent simplicity, there.

have been many attempts to provide satisfactory bimetal starting andoverload controls for electric motors. One example of such a bimetalstarting control is-shown in Fig. 2 of the Werner Patent No. 2,117,123.A number oi' dimculties have prevented the Wide use of such a control.

@ne of the most troublesome factors is the wide range of current valueswhich must be conducted by the starting control. In such bimetalstarting controls, the motor current is used to iirst rapidly heat thelloimetal operated starting switch until the starting circuit is opened.The motor current must then continue to heat the bi-v metal operatedstarting switch to keep the startf ing circuit open throughout theremainder of the running period oi the motor. It is well known that atthe point of use or connection of a device connected to acommercialsupply line, the voltage varies widely depending upon the conditions ofthe system. For example, a nominal 110 volt circuit may deliver currentat a voltage of from 9D to 120 or 125 volts.

By testing such himetal starting controls, it has been found iisuflicient heat is provided for the starting control to give properstarting on a 9G volt current supply, that too rapid heating will occurupon a 120 volt supply. Or if the heating is reduced suiliciently toprevent overheating on 120 volts, the heating will be insufficient tocause the bimetal to hold the starting circuit open when the voltagesupply drops to 90 volts. Even where the power supply and individualpower circuit does not vary to this extent, a manufacturer of startingcontrols is still confronted with this problem, since the equipment hebuilds for a nominal 110 volt circuit may be used either upon a powercircuit which frequently supplies current at the point of delivery at 90volts o1' upon another circuit which may supply current at the point ofdelivery at 120 or 125 volts. It has, in the past, also been necessaryto provide for the manufacture of several different variations ofstarting controls to accommodate diiierent current frequencies becausethe power supply in this country employs in different communities,25,-50 and 60 cycle current. It is therefore desirable that one startingcontrol be provided which will operate satisfactorily upon a widevariation of voltages and frequencies.

Another diiculty with such bimetal starting and overload controls isthat the operation varies 2 according to changes in the room orenvironment temperature. Still another difficulty is that the overloadprotector may reset before the starting control resets.

It is an object of my invention to provide a practical bimetal startingcontrol for controlling the energization oi the phase winding in whichthe bimetal will not be overheated under any operating condition.

' It is another object of my invention to provide a heating arrangementfor a bimetal starting control which will supply sutllclent heat toprovide proper operation under all expected conditions without supplyingexcess heating under any conditions.

It is another object of my invention to provide a simple inexpensivestarting control in which the timing is kept within a desirable rangeregardless of the variations in voltage conditions.

It is another object of my invention to provide a starting control whichwill operate satisfactorily upon current of 25, 50 and 60 cycles.

It is another object of my invention to provide a starting control inwhich the timing is kept Within a desirable range regardless of changesln the room or environment temperature.

It is another object of my invention to provide means for keeping themotor overload protector tripping point within a desirable rangeregardless of the change in the room or environment temperature.

It is another object of my invention to provide a bimetal starting andoverload control in which the overload will reset at the same time orearlier than the starting control.

It is another object of my invention to provide an improved support andarrangement of the ends of a bimetal strip.

It is another object of my invention to provide l means for reducing thevoltage drop and heating produced within an electro-thermal startingcontrol during the starting period of the motor.

It is another object of my invention to provide a thermal snap-actingstarting control which will trip quickly upon vthe application of asmallamount of heat.

When the electric motor is connected to certain loads, such as forexample, the compressor of a refrigerating system, the starting loadupon the motor increases with the environment temperature and it isdesirable that the lengthof the motor starting period be increased withincreasing temperature to compensate for the slower acceleration`of tliemotor to the optimum phase switching speed.

- starting circuit open during the running period of the motor.

A bimetal thermal overload with an auxiliary heater is provided withgreater heat storage capacity than the starting control, so that thestarting control will reset before the thermal overload will reset. Theheating of the starting l bimetal and its auxiliary heater produces atemperature controlled amount of heat within the switch casing toprovide a temperature which varies less than the environment temperatureso as to reduce the variation in the tripping value of the overloadcontrol to a minimum.

The starting bimetal is compensated for variations in its environmenttemperature by a second bimetal strip. Where the motor is to be used todrive a refrigerator compressor or a load having similar characteristicsin which the starting period should increase with an increase intemperature, this bimetal is made over-compensating so as to increasethe starting time as the environment temperature increases.

The contacts are arranged so that the bimetals are substantiallystraight when cool. Each bimetalv is column loaded to provide a snapaction. The short-circuited stationary contact which coomrates with thestarting bimetal system, is located outside the snap action range tofacilitate the periodic opening and closing of the shortcircuitingcontact during the running period of the motor. Each of the ends of eachof the bimetals preferably is provided with a 18D degree edgewise turnand a lateral bend which is connected to the anchorage and is used toapply the adjustable column loading to the bimetals.

Further objects and advantages of the present invention will be apparentfrom the following description, reference being had to the accompanyingdrawings, wherein a preferred form of the present invention is clearlyshown.

In the drawings:

Fig. 1 is a horizontal sectional view taken along the lines i-i of Figs.2 and 3, showing one form of control embodying my invention;

Fig. 2 is a sectional View taken along the lines ii-t of Fig. l;

we. 3 is a sectional view taken along the lines 3 8 of Figsl and 2;

Fig. 4 is a diagram including a refrigerating system and a wiringdiagram of the motor and control system connected for the starting ofthe motor in which the energized portions are indicated by heavy linesand the deenergized portions by light lines;

Fig. 5 is a wiring diagram similar to Fig. e showing the changedconnections and circuits at the completion of the starting period;

Fig. 6 is a Wiring diagram similar to Figs. d and showing the other formof connection and circuit assumed intermittently during the runningperiod:

Fig. 'Z is aternperature-movement diagram of the starting bimetalillustrating the movement of the starting contact with the rise and.fall in the temperature of the bimetal; vand Fig. 8 is a graphillustrating the length of the starting period at difierent temperaturesand voltages and also the starting contact trip and reset pressures atdifferent temperatures.

Referring now more particularly to Fig. 4, there is shown an electricmotor-2B having a main or running winding 22 and a phase or startingwinding 2t. This motor 2t is shown connected diagrammatically to drive arefrigerator compressor 25 which withdraws evaporated refrigerant fromthe evaporator 2l and forces the compressed refrigerant into thecondenser 2Q where it is liquened and returned to the evaporator 2liunder the control of a suitable valve. IThe evaporator 2l is employed tocool the medium within the compartment 3i. During idle periods of therefrigerating system the evaporator 2i is warmed up and if the idleperiod is sufficiently long it will reach Ithe room temperature. Theevaporation of the liquid refrigerant in the evaporator 27 produces apressure in accordance with its temperature. The pressure in thecondenser also increases as the environment temperature increases. Thiscauses the starting load upon the compressor to increase as theenvironment temperature increases.

The electric motor 2t is supplied with electric energy through thesupply conductor 2t which connects to the common junction of thewindings 22 and 2d and the supply conductor 28 which connects throughthe control switch 33 to the starting and overload control designatedgenerally by the reference character Sii. To provide a greater startingtorque, the phase winding 2li is shown connected by the conductor 83 toa condenser or starting capacitor 23 to make the motor a capacitor startmotor. However, if high starting torque is not required this startingcapacitor 2t may be omitted. When so omitted the motor 2t is an ordinarysplit phase motor.

The overload protector The conductor 2@ through the switch 33specilically connects to an L-shaped mounting bracket 32 (see Figs. 1 to3) having its lower portion beneath the switch mounting base 55d. Thislower portion is riveted to the base 3d by a hollow rivet threaded toreceive the fastening screw 35 which fastens the supply conductor 28 tothe bottom of this Lshaped mounting bracket 32. The upper portion of theL-shaped mounting bracket 32 extends upwardly through a slot in theswitch mounting base 3d. To it is fastened by Welding or soldering oneend of the coiled electric heater 36. The other end of this electricheater 36 is supported by an L-shaped stationary contact 40 whichextends through the base 3 and is riveted thereto. In an engagement withthe stationary contact 4t is a movable contact 42 carried by the middleof a column loaded bimetal strip it which serves as the actuatingbimetal of the overload control. The stationary contact iii is solocated that when engaged by the movable contact t2 the bimetal strip Mwill be held substantially straight. v

To rmly support the bimetal strip it the ends are welded to the upturnedends t5 and d8 of bow to the left at its mid-portion such plain anchoredends of the strip would tend to bend counterclockwise at the top andclockwise at the bottom so as to i'orce the midpoint of the bimetalstrip 44 to the right.

To prevent this opposition and to make both effects supplement eachother I provide edgewise curves or bends 43 and 45 through an angle 'of180 degrees at each end of the strip 44 and bend eachof these turnedportions at right angles and weld their ends 41 and 49 to the upturnedends 48 and 48 oi the main bracket 50. Upon heating this causes thebimetal ends to accentuate thc bowing to the left of the mid-portion otthe strip 44 by bending clockwise at the top and counterclockwise at thebottom and this makes it possible to make the control smaller.

The upturned end 48 is provided with an adjusting screw 52 which may beadjusted to provide any desired column loading upon the bimetal strip 44by engaging the free portion of this welded right angled portion 49 ofthe strip 44. In this column loading the right angled portion .49 actsas a compound cantilever spring for applying the column loading indirect alignment with the strip 44 when in the closed position. Thiscolumn loading insures a snap opening and closing of these contactswhich can be separately adjusted.

The adjustment provided by the screw 52 varies the force required toclose the overload contacts 42 and 4U. This force is obtained by thecooling of the bimetal strip and thus the adjusting screw 52 may be setto vary the closing temperature of the overload contacts. The opening ofthe contacts is adjusted by moving the stationary contact 40 toward oraway from the strip 44. Moving the contact 40 toward the strip 44 willreduce the contact opening temperature while moving the contact 40 awayfrom the strip will increase the contact opening temperature. Theinitial curvature, type, width, thickness and length of the bimetalstrip 44 and the resistance of the auxiliary heater 36 may be varied toprovide the proper overload tripping and resetting characteristics fordifferent motors.

The starting control The upturnedend 48 of the bracket 50 supports thelower end of the starting bimetal strip E0 which, like the overloadbimetal strip 44, has its end portions turned edgewise 180 degrees, asindicated by the reference characters 6I and G3, and then at rightangles for similar reasons. The end of the right angled portion 59 iswelded to the upturned portion 48 and is provided with a set-screw 68for applying a resilient column loading to the strip 60. The rightangled portion 59 acts as a compound cantilever spring which applies thecolumn loading in substantially direct alignment with the strip 60 whenin contact with the starting contact 18. At the upper end of the strip60 the right angled portion 85 is Welded to the upturned end 84 of aseparate bracket 66 extending alongside of the bracket 50 and likewiseriveted at two points to the switching mounting base 34. It is providedwith a longitudinal stiilening rib.

At its midpoint the starting bimetal strip 6!) carries a double-endedcontact which when the strip 53 is cooled engages with considerablecontact pressure the starting contact member 18. The starting contactmember 18 is in the form of an L-shaped bracket extending beneath theswitch mounting base 34 and is riveted thereto.

tends through the switch The auxiliary heater Connected to the bracket65 is one end of an electric heater 56 which extends along the outerside of the starting bimetal strip and has its other end fastened to theL-shaped back contact member 14. This back contact member 14 exmountingbase 34 and is riveted thereto. On its bottom face it is provided with abinding screw 15 which connects this back contact member 14 with theconductor 88 of the main winding circuit.

The compensating bimetal The starting bimetal strip 3l is also providedwith a compensating bimetal strip |2| which may either exactlycompensate or under or over compensate for the eilects of environmenttemperature upon the starting bimetal strip 33. This compensatingbimetal strip I 2| is bent inwardly at its central portion and fastenedto the strip 80 by the double contacts 10 which may be riveted or weldedtogether. The compensating bimetal strip I2| extends in both directionsfrom its mid-portion spaced away from the strip 50 a suillcient distanceto prevent it from receiving any material amount of heat from the strip80. Each of th-e ends of the compensating strip 2| is provided with anextremely small projection |23 which bears lightly against the adjacentend portions of the starting bimetal strip 40. The compensating bimetalstrip |2| is notched at each end as indicated by the reference character|25 so as to avoid contact with the right angled portions 59 and 85 ofthe starting bimetal strip B0 and the 4upturned portions 48 and 84 ofthe brackets 60 and 56. The surface contact resistance of theprojections |23 upon the ends of the starting bimetal strip 60 is sohigh that no appreciable amount of current flows through thecompensating strip I2| The compensating strip |2I is made of suchinitial curvature, length, width, :thickness and type of bimetal that itwill pro'ide just the amount of compensation desire The switch mountingbase 34 is made of some suitable electrical insulating material and ispreierably mounted within a casing 90 likewise of insulating material.The mounting base 34 is held in place against the shoulders 94 providedin the corners by -the projections 92 upon the sides of the casing 9U.

Current flow through the control With this arrangement, when the motor20 is first connected to the power line through the closing of theswitch 33, as illustrated by the heavy lines in Fig. 4, the current willflow 'from the supply conducto; 28 through the switch 33 to the bracket32, thence through the heater 35 alongside the overload bimetal strip 44to the stationary contact 40 and the movable contact 42. From this pointthe current will divide and flow in opposite directions throughout theoverload bimetal strip 44 until it reaches the points 7 at which it iswelded to the upturned ends Il and I8 of the main bracket B0.

The characteristics of the heater 3G and the characteristics andadjustment of the 'bimetal strip 44, andthe position of the stationarycontact d will determine the current values which will cause theoverload bimetal strip l! to trip open to deenergize the motor 2li uponan overload. The column load imposed by the setscrew 52 will determinethe temperature to which the overload bimetal strip M will iall and thusthe resetting time required before it will snap to its closed position.This resetting time must be made longer than the resetting time of thestarting bimetal strip St. By arranging the contacts so that theoverload bimetal strip d4 is held straight when closed, the trippingcurrent can separately be adiusted by bending or adjusting the locationof the stationery contact dt, since the column loading has little eectas long as the bimetal lstrip llt is straight. The resetting time andtemperature can be separately adjusted by adjusting Ithe column loadingthrough the adjusting screw E52.

From the ends of theoverload bimetal strip it current will flow throughthe main bracket 5u to'the point at which the right angled portion 5s ofthe starting bimetal strip d@ is welded to the u-pturned end dd. Allthis current will then pass upwardly through the lower portion o1 thestarting bimetal strip 6i) to the double contact l@ at its mid-point.There more than half the current will flow through the contacts i@ andi8 to the starting or phase winding circuit including conductor Si?,capacitor 23 and the phase winding 2d to the supply conductor 2t. The remainder of the current will flow through the up per portion of thestarting bimetal strip t@ to the bracket te and thence through theheater 5t to the back contact member it which connects to the mainwinding circuit including the conductor 88 and the main winding 22 whichconnects to the supply conductor it.

Operatimz Upon the initial starting of the motor, the bimetals d@ and etwill be at room temperature and the control will be in the positionsshown in Figs. 1 to 4. This is indicated by the point i2@ upon thediagram shown in Fig. 7, although it is held substantially straight bythe starting contact i8, at room temperature. The initial curvature ofthe starting bimetal strip G@ tends to bow it to the left so as to presstightly against the starting contact i8. The flow of current throughthis starting bimetal strip dii will gradually raise its temperature asillustrated by the vertical line extending up from the point i253 inFig. 7 to cause it to rapidly reduce its tendency to bow to the left.The starting bimetal stri-p d@ is of such length, thickness, width,initial curvature and characteristics that at the most desirable timefor terminating the starting period it will become straight.

When the temperature gets so high that the pressure against the startingcontact itl reaches zero, the starting bimetal strip d@ will snap andbow to the right to the position shown in Fig. 7 due to the columnloading and the temperature pointing action of the bimetal. Thissnapping or tripping temperature is indicated by the referencecharacter; V22 and the movement of the contact it at this temperature isdesignated by the horizontal line connecting the point @22 and the pointE26. r This snapping or tripping temperature may be raised or lowered bybending the starting contact away or toward the starting bimetal stripB0, thus increasing or reducing the length of the starting period. Byarranging the starting contact 18 so that the strip tt is heldsubstantially straight during the starting period, there issubstantially no resistance to the movement of the starting contact '18and less heating of the bimetal strip is required and a heavier bimetalmaterial may be used. It also reduces the energy consumed by thestarting control during the starting period as well as during therunning period, thus increasing the net amount available for the motor.The starting bimetal strip Bil is also less likely to overheat undersuch an arrangement.

r The compensating bimetal strip li is so ar-s ranged that when coolingits end portions bow to the left thus forcing the end portions of thestarting bimetal strip t0 to the left and at the same time themid-portion of the strip t@ is pulled to the right. As shown in Fig. 8,the starting contact tripping pressure is lowest when the temperature islowest and this pressure rises in almost a straight line as thetemperature rises. Without this compensating bimetal the startingcontact tripping pressure would fall as the temperature rises therebyreducing the starting time or starting period as the temperatureincreases. While this may be satisfactory for some applications, such aswhen a motor is driving a device working upon viscous uid, whichprovides decreasing opposition to movement as the temperature increases,it is not suitable for many other applications and often the rate ofchange is not suitable even though the variation may be in the rightdirection. Hence the bimetal strip i2! may be under-compensating forsuch loads.

` For many other applications the load does not change materially withtemperatures and therefore the starting contact tripping pressure shouldbe uniform. In such a case the compen-l sating bimetal strip im is madeof such a length,

width, thickness and characteristics that it.

exactly compensates for the eect of environment temperature upon thestarting bimetal strip 6B. This would produce a substantially straighthorizontal line for the starting contact tripping pressure dn the graphFig. Y8. It would also provide a substatnially straight horizontal linefor the length of the starting period or starting time at differenttemperatures and diierent voltages.

Some starting loads, for example refrigerator compressors, are heavieras the ambient or environment temperature rises. Under such conditionsit will take longer for the motor to reach the proper switching speed atwhich the phase winding should be disconnected. For such loads thecompensating bimetal strip i2! should be of such length, width,thickness, initial curvature. and characteristics that it willover-compensate for the eiect of environment temperature on the startingbimetal strip Gd to produce a rising contacttripping pressure as shownin Fig. 8. This also provides a gradual increasing starting time withrising ambient temperatures at different voltages. 'Ihe starting time isinherently lengthened at low voltages since the heating effect is slowerand this is desirable since the motor has less power under low voltagecon' ditions and requires more time to reach the optimum speed forswitching. Thus by the use of an over-compensating bimetal strip i2i thestarting bimetal strip tt will provide a starting 9 time,which isadjusted to the starting load of thev refrigerator compressor 25 and thetime required for the motor to reach its optimum speed for switchingunder all temperature conditions.

The starting bimetal strip 60 travels rapidly away from the startingcontact 10 under the force oi' the snap action column loading andreaches the back contact '|4 without a pause. In this operation thephase winding 24 is disconnected from the power source 28 for theremainder of the running period of the motor. The column loading of thebimetal strip 60 is such that at the tripping temperature indicated bythe horizontal line |22 to |24, the contact 10 will just be in contactwith the back contact 14 without any contact pressure. In action,however, due to inertia, the contact 18 will strike the back contact 14with considerable force. This contact immediately shunts both the heater59 and the upper half of the starting bimetal strip 60 and arranges thecircuits as shown in Fig. 5. The main winding current ilowing throughthe lower half of the starting bimetal 60 to the back contact 'I4 isinsuillcient to prevent the bimetal 60 from cooling slowly but it issulcient to prevent rapid cooling. This causes the bimetal 60 togradually creep away from the back contact 'I4 nearly to the positionillustrated in Fig. 6.

In creeping away from back contact 14 the movement soon is opposed bythe gradually increasing resistance due to the column loading of thebimetal strip 60. This movement, however, is beyond the snap actionrange and is represented by the curve between the points |24 and |26 inFig. 7 which shows that as the temperature falls the movement becomesless, due to this increasing resistance. The snap action range is:indicated by the horizontal line between the points |28 and |30.However, as soon as the bimetal contact 1|) leaves the back contact 'i4the shunt for the heater 56 and the upper portion of the bimetal strip60 is opened and the current again ows through the upper portion of thestrip 6D and the heater 56. This heat is sufficient to slow down themovement of the strip 60 and to stop it and reverse its movement so thatit again moves into contact with the back contact 74. This reversaltakes place at some point on the curve between the points |24 and |26 inFig. 7. The point of reversal is not fixed but depends somewhat upon theenvironment temperature which governs the rate of cooling of the upperportion of the bimetal strip 60 and the heater 56 as well as the speedat which the temperature is restored.

This contacting of the contact 1U with the back contact 14 and thesubsequent creeping away and again contacting the back contact takesplace repeatedly during the normal running period of the motor. In Fig.7 this is represented by repeated movements from the point |24downwardly a. variable distance along the line toward the point |26. Itis through this cycling on the back contacts that the temperature of thebimetal strip 60 is kept substantially constant during the normalrunning period and is prevented from overheating. The resetting time ofthe starting bimetal strip 6|) is regulated by this cycling temperature.This cycling temperature may be raised or lowered by bending the backcontact i4 6|) or by increasing or reducing the column loading byadjusting the set-screw B8 or both. It also is provided through thismeans with sumaway or toward the strip i0 cient heat to prevent it fromsnapping backto the starting position. This cycling on the back contacttakes place outside of the snap action range provided by the columnloading of the strip lli. The cycling on the back contact providesthermostatically controlled heating oi' the interior of the casing lllso as to reduce the variations in temperature therein due to changes inroom temperatures. As shown in the graph, Fig. 8, the starting contactresetting pressure does not vary because the column loading o1' thebimetal strip which determines the resetting pressure does not vary withtemperature changes. When the motor circuit is opened to shut oi! themotor by opening the'switch Il the bimetals and heaters will cool. Incooling the bimetal it will reach the point of maximum resistance o! thesnap action column loading applied to it immediately after it passes incooling below the point |23 in Fig. 7. It will then cool without muchmovement until it cools to the point designated by the referencecharacter' |25 where it enters the snap action zone or range ofmovement. Upon passing this point without any appreciable cooling thebimetal strip 80 will snap immediately into contact .with the startingcontact 18. This movement is designated by the horizontal line extendingfrom the point, |28 to the point |30 located on the vertical linebetween the points |20 and |22. The strip 8l will cool without furthermovement.

Should there be an excessive current flowl through the circuit, the 60will cycle on the back ing its temperature until bimetal strip 44 isheated starting bimetal strip contact thereby limit-v the thermaloverload to its tripping point so as to apply a column loading to thethermal overload bimetal strip 44 rwhich will insure that theoverload'contacts will not close until after the starting bimetal strip60 has reset to its initlal position.

This application is a continuation-impart of my copending applicationsS. N. 473,892, tiled January 29, 1943, now Patent No. 2,451,535, issuedOctober 19, 1948, and S. N. 552,166, tiled August 31, 1944, now PatentNo. 2,417,912, issued March 25, 1947.

While the form of embodiment of the invention as herein disclosed,constitutes a preferred form, it is to be understood that other formsmight be adopted, as may come within the scope of the claims whichfollow.

What is claimed is as follows:

1. A control comprising a bimetal strip portion having one portionturned edgewise substanmeans for rigidly supporting said strip portionat the one terminus of said turned portion'and at a portion separated asubstantial distance from the opposite terminus of said turned portion,and a control device operably connected to and operated by the part ofthe strip portion between said points of support.

2. A control comprising a bl'metal strip portion provided with asubstantially straight portion at each end of which are degrees edgewisedirections, means for supporting said strip portion solely by saidturned portions, and a control device operably connected to and operatedby said straight portion.

3. A control including a bimetal strip portion,

' a, normally stationary contact positioned to hold bimetal stripportion in response to ambient tem-f peratures, and means for heatingthe nrst men tioned strip portion independently ofthe second.

s. A control including a bimetal strip portion, means for supportingsaid strip portion at two separated points, with the strip portion freeto bend between the points of support, contact means connected to saidstrip portion between said points of support, compensating meansincluding a second bimetal strip portion having an operative connectionwith said nrst strip portion to apply a load thereto substantially inaccord ance with its own temperature, and means for heating said firststrip portion substantially independently of said second strip portion.

5. A control including a bimetal strip portion,

means for supporting said strip portion' at two `separated. points, withthe strip portion free to bend between the points of support, contact.means connected to said strip portion between said points of support,compensating means in= cludina a second bimetal strip portionoperatively connected to said first strip portion adiacent said contactmeans and atleast one other point separated therefrom, and means forheating said nrst strip portion substantially independently of saidvsecond strip portion.

6. A control including a strip portion a normally stationary contactpositioned to hold the strip portion substantially straight when contactis made, means for applying a column loading to said strip portion sothat it is in substantial direct alignment with the strip portion whencontact is made for providing a snap=acting movement ci the strip awayfrom the contact substantially without opposition from the columnloading, said strip portion being provided with means tending to forceit toward and away from said contact, and temperature responsive meansfor applying el load to said strip portion in accordance with ambienttemperatures.

7. A control comprising a bimetal strip portion adapted to move in a rstdirection when 'cooling and in a second direction when heating,

a normally stationary contact positioned to stop the movement of thestrip portion upon cooling, a thermal means responsive to environmenttemperatures for applying an increasing load upon 12 l said stripportion in said second direction 'upo cooling. and means for heatingsaid strip portion with electrical energy.

8. A control comprising a bimetal strip portion having one portionturned edsjewise substantially 180 degrees, rigid'supporting means forrigidly supporting said strip portion substantially at the one terminusof said 180 degree portion, said bimetal strip portion having a secondportion extending substantially straight from the opposite terminus oisaid 180 portion and a control device operatively connected to andoperated by said second portion of the strip portion remote from 'said180 portion.

9. A control comprising a bimetal strip portion having a substantiallystraight mid-portion at one end of which is a 180 degree edsewise turn,said one end adjacent the terminus oi the 180 degree turn being bentsubstantially at right angles to said mid-portion, means for applying acolumn loading to said portion bent at right angles, and a controldevice operably connected to and operated by said mid-portion.

10. A control comprising a bimetal strip portion having a substantiallystraight mideportion at each end of which are 180 degree edgewise turnsin opposite directions of rotation, each ci the ends adjacent theterminus of their 180 degree turns being bent substantially at rightangles to said mid-portion, means for applying a column loading to saidportions bent substantially at right angles in substantially directalignment with said mid-portion, and a control device operably connectedto and operated by said j mid-portion.

REFERENGES @MED The following references are of record in the ille ofthis patent:

UNITED STATES PATENTS Number Name Date 1,578,119 Hall Mar. 9, 19262,016,244 Gregory Oct. 1, 1935 2,095,579 Werner Oct. 12, 1937 2,132,888Werner Oct. 11, 1938 2,133,309 Schmidinger Oct. 18, 1938 2,175,032Schaefer Oct. 3, 1939 2,177,671 Schmidinger Oct. 31, 1939 2,207,422Vaughan et al. July 9, 1940 2,254,054 Vaughan et al Aug. 28, 19412,255,169 Ireland Sept. 9, 1941 2,288,640 Paulus July 7, 1942 2,332,518Kooi Oct. 26, 1943 2,374,967 Alexander May 1, 1945 2,379,802 Stickel Juy3, 1945

